Wilms tumor, also known as nephroblastoma, is the most common cause of pediatric renal malignancy in the United States, accounting for 95% of renal tumors in this age group, with an estimated annual incidence of 7 cases per 1 million children younger than 15 years. This incidence is believed to be fairly uniform globally as well, with a slight increase among those of African descent and a slight decrease among patients of Asian descent compared to those of Northern European descent. Wilms tumors are 5% of pediatric malignant tumors (primarily in lymph nodes and lung). The mean age at presentation / diagnosis is 3 years for sporadic cases and 2 years for hereditary cases. While it is primarily a sporadic disease (< 2% hereditary), 1 in 10 will be a part of a multiple malformation syndrome such as WAGR syndrome, Beckwith-Wiedemann syndrome, or Denys-Drash syndrome, to name only a few. Children with concurrent congenital anomalies (eg, genitourinary abnormalities, aniridia) tend to be diagnosed at an earlier age.

Children most commonly present with an asymptomatic abdominal mass. Prior to diagnosis, 1 in 4 patients may develop a complication from tumor invasion of the kidney such as hematuria, abdominal pain, or hypertension. A small group can present more acutely in the setting of subcapsular hemorrhage with pain, rapidly enlarging abdominal mass, anemia, hypertension, and, in some cases, fever.

The majority of Wilms tumors are isolated lesions, with only 1 in 10 patients with multiple lesions in a single kidney and between 5%-7% with bilateral kidney involvement.

Wilms tumor has rarely been reported in adults. This summary focuses on children.